It is common that mining for extraction of ore bodies is carried out in drifts that are relatively low and narrow. For example, when extracting ore it is for economical reasons often desirable that the extraction of ore is carried out in such a manner that preferably only the ore body is extracted, thereby reducing the amount of surplus rock that must be taken care of to the largest possible extent, i.e. as little as possible of surrounding rock/ore should be brought with the extracted ore for further treatment.
Ore bodies can be disposed in relatively thin layers (order of magnitude of 1-2 meters thick), which has as result that extraction of thin ore bodies and/or where only a thin portion of the ore body comprises a desired content of ore, extraction can be carried out with drifts of very low heights as result, with consequent demands on the rock drilling rig to allow extraction of ore with a limited height.
During extraction of ore of the above kind, but also in other situations where rock drilling is carried out in narrow/low drifts, as well as during rock drilling in general, it is often desirable, and oftentimes a requirement, that walls and roof in an already drilled portion of a drift are reinforced to ensure that rock/stone portions can not come loose and fall down with the risk for injuries on man and machine as result.
This reinforcement is often performed by installation of rock bolts, in general according to some predetermined pattern, such as e.g. with a certain largest mutual distance between the bolts, where the rock bolts after installation secures the rock. Installation of rock bolts of this kind, which installation usually consists of drilling of a hole with subsequent installation of the rock bolt in said hole, is often carried out by means of machines.
This rock reinforcement, however, usually requires a certain smallest bolt length which, when the drifts are low/narrow, has the result that the length of the bolt in addition to the dead length of the bolt unit, i.e. the length behind the rock bolt that is required for a bolt installation to be able to take place, exceeds the height/width of the drift, with the result that manual actions taken by the operator often are required.
For example, presently occurring bolt units, even though these often are designed especially for use in narrow drifts, can require that the operator in a plurality of stages in the operation during the bolt installation operation actively must perform a plurality of stages of the operation at the position for bolt installation, and thereby at a position under unsecured rock. Examples of such manual actions to be taken consist of joining/changing drill rod, and also manual insertion of the rock bolt in the drilled hole at least to some extent before the space behind the rock bolt is sufficient to enable the remaining part of the rock bolt to be inserted in the drilled hole with the aid of the machine.
Consequently, there are a plurality of stages in the operation where the operator can be forced to work under unsecured rock, and also stages in the operation where drill rod and/or rock bolt are worked in the partly or completely drilled hole, with the risk for portions surrounding the drill hole loosening and falling down with the risk for injuries as result.